In recent years, various kinds of video cameras have been used that provide still and/or motion pictures and use a solid-state image pickup element such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) at the image pickup plane. The solid-state image pickup elements have become more miniaturized each year by technological advances, and an accompanying miniaturization of the imaging lenses of the video camera has been demanded. Also, there has been an increasing demand for reducing manufacturing costs. Furthermore, the number of pixels in the image has been increasing. This, in turn, has produced a demand for higher resolution and higher performance imaging lenses.
Japanese Laid-Open Patent Application H10-301022 describes exemplary imaging lenses for such cameras that include only three lens elements, including plastic lens elements, in order to achieve miniaturization and reduction of manufacturing costs.
As stated above, recent image pickup elements have been highly miniaturized and provide an increasing number of pixels accompanied by demands for higher resolving power and miniaturization of the imaging lenses used with such image pickup elements. On the other hand, in optical systems employing an image pickup element, optical elements, such as cover glasses and cut-off filters, are often placed between the final image-side lens surface and the image pickup element. This, in turn, requires allowing space in terms of length along the optical axis for such optical elements between the final image-side lens surface and the image pickup element.
In order to realize both miniaturization and adequate length, it is desirable to increase the distance between the final image-side lens surface and the image pickup element relative to the total length of the imaging lens. Although the imaging lenses described in Japanese Laid-Open Patent Application H10-301022 have good overall performance, the imaging lenses of this Japanese published application provide relatively little space for optical members such as cover glasses and cut-off filters. Additionally, these imaging lenses provide relatively narrow field angles of forty-three degrees so improvement in field angles is also desired.